Which muscle is the primary muscle of supination?

Which muscle is the primary muscle of supination?

• A. Biceps Brachii
• B. Brachialis
• C. Triceps Brachii
• D. Pronator Teres

Answer: (A)

Supination is the action of rotating the forearm so the palm faces upward. The biceps brachii is the primary muscle that drives this motion, especially when the elbow is flexed. Its tendon attaches to the radius, so when the biceps shortens it not only helps bend the elbow but also twists the radius to turn the hand outward, giving a strong supination effect. The other muscles here don’t promote that rotation: the brachialis mainly flexes the elbow with no forearm twist, the triceps extends the elbow, and the pronator teres actually turns the palm downward (pronation). Because of its direct attachment to the radius and its powerful rotational effect when the elbow is flexed, the biceps brachii stands out as the best answer for the primary supinator.

Supination is the action of rotating the forearm so the palm faces upward. The biceps brachii is the primary muscle that drives this motion, especially when the elbow is flexed. Its tendon attaches to the radius, so when the biceps shortens it not only helps bend the elbow but also twists the radius to turn the hand outward, giving a strong supination effect. The other muscles here don’t promote that rotation: the brachialis mainly flexes the elbow with no forearm twist, the triceps extends the elbow, and the pronator teres actually turns the palm downward (pronation). Because of its direct attachment to the radius and its powerful rotational effect when the elbow is flexed, the biceps brachii stands out as the best answer for the primary supinator.